Jet aircraft propulsion systems, such as those that power modern commercial aircraft, typically include an annular bypass air duct situated substantially concentrically about an engine core. The bypass air duct may be separated from the engine core by an inner fixed structure (“IFS”). The IFS defines the interior aerodynamic surface of the annular bypass air duct, and surrounds the engine core forming a substantially annular enclosed space (or “core cavity”) around the engine core. The engine core may generally comprise a compressor, a combustion section, and a turbine as its primary components. Surrounding the engine core and within the core cavity, numerous support systems (such as fuel, oil and hydraulic systems) support these primary components and may operate at very high temperatures. The core cavity may therefore require substantial cooling during operation. To this end, one or more vents may extend through the IFS to channel cooler air flowing within the bypass air duct into the annular enclosed space surrounding the engine core.
Several thrust reverser components may be coupled to the IFS. The components may include one or more blocker doors as well as one or more drag links associated with each blocker door. The drag links may be attached to the blocker doors and may form part of a kinematic mechanism to deploy the blocker doors during thrust reverser operation. The drag links may be attached to the IFS via a drag link fitting.
Drag link fittings and vent holes may contribute to drag and may hinder efforts to attenuate noise in the bypass air duct. Drag link fittings and vent holes can be situated proud of the surface of the IFS and lie in the air stream of the bypass air duct, thus interrupting air flow and creating drag. The IFS may typically comprise an acoustic treatment or noise suppressing structure. This structure may comprise a perforated top layer and a bottom layer, between which a honeycomb shaped core may be disposed. Noise may be attenuated within the cavities formed by the honeycomb shaped core. Where the IFS is penetrated by a drag link fitting or a vent, however, no noise suppressing structure may be included. Instead, to counteract stresses, the IFS surrounding a drag link fitting or vent is typically constructed of a structural material that does not include the perforated top layer and sound attenuation features.
In addition, as jet engines continue to increase in size, power, and/or efficiency, engine operating temperatures tend to increase as well. To compensate for these high temperatures, the number and size of ventilation apertures (or vents) formed between the bypass air duct and the engine core cavity have increased, lessening the area available for acoustic treatment as well as increasing drag over the IFS. There is, then, a need for an. improved design which minimizes drag and/or improves sound attenuation.